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Modifying food texture is a valuable approach to enhancing the quality of life for patients with dysphagia. Incorporating thickened soy protein-based liquid systems (SPLS) into their diet not only improves protein intake but also promotes safer swallowing. However, the properties of thickened SPLS are crucial for safe swallowing, may vary depending on the conformation of the thickened polysaccharides used. In this study, SPLS with different levels of thickening were prepared using xanthan gum, pectin and guar gum. The influence of polysaccharide conformation on the rheological (shear and extensional) and tribological properties of thickened SPLS was investigated. The results revealed that xanthan gum-thickened SPLS exhibiting the highest shear viscosity (110.073 Pa.s) and extensional viscosity (7.405 Pa.s), which increased with polysaccharide concentration. Meanwhile, xanthan gum possessed the strongest lubricating properties. These results shed light on the development of plant protein-based solutions for dysphagia management.

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In this study, we delve into the intricacies of elastoviscoplastic (EVP) fluids, particularly focusing on how polymer additives influence their extensional behavior. Our findings reveal that polymer additives significantly alter the extensional properties of the EVP fluids, such as relaxation time and extensional stresses while having negligible impact on the shear rheology. Interestingly, the modified fluids exhibit a transition from yield stress-like behavior to viscoelastic-like behavior under high extensional rates, ultimately leading to destabilization under extreme deformation. This research enhances the fundamental understanding of EVP fluids and highlights potential advancements in applications, especially in precision-demanding fields like 3D printing.

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The prevalence of xerostomia, the sensation of dry mouth, is estimated at 20 % in the general population and up to 50 % in older adults. Saliva plays different roles during bolus formation: lubrication, mixing, coating, hydration, dissolution, and comminution of food particles. This study proposes and tests artificial saliva formulations mimicking human saliva rheological and sensory perceptions. Shear and extensional rheology were assessed to select the type of formulation closest to saliva rheological characteristics. After evaluating three alternative sources, an extract simulating saliva rheology was produced from flax seeds. Friction coefficient and rheological properties, such as flow curves, relaxation times, and Trouton ratios, were compared favorably with human saliva. The sensory evaluation demonstrated that flaxseed extracts induce perceived mouth hydration, slipperiness, and adhesion exceeding that of human saliva. The flaxseed extract proposed in this can i) be used to study in vitro food oral processing and ii) pave the way to novel natural salivary substitutes to alleviate the symptoms of xerostomia.

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Processing of electrode slurry, which is highly non-Newtonian fluid, is a critical step in the mass production of lithium-ion batteries (LIBs). While extensional flow plays an important role in the electrode slurry processes such as coating, most previous studies have focused only on the shear rheology, due to the lack of a reliable method to measure the extensional rheological properties of the slurry. Here, it is demonstrated that the extensional rheological properties of the anode slurries can be successfully characterized using the stop-flow-dripping-onto-substrate/capillary break-up rheometry (SF-DoS/CaBER). Using this system, it is observed that the extensional rheology of the anode slurry is significantly affected by the blend ratio of the natural and synthetic graphite, as well as the binder and conductive concentrations. Furthermore, the shear rheology-based model predicts much shorter pinch-off times than those measured experimentally, indicating that the yield-stress of the anode slurry is much larger in extensional flow than in shear flow.

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A shear-thickening polysaccharide from the New Zealand Black tree fern (Cyathea medullaris, commonly known as mamaku) extracted from different age fronds (stage 1: young, stage 2: fully grown and stage 3: old) was characterised in terms of structure and rheological properties. Constituent sugar analysis and 1H and 13C NMR revealed a repeating backbone of -4)-ß-D-GlcpA-(1 â†’ 2)-α-D-Manp-(1→, for all mamaku polysaccharide (MP) samples from different age fronds without any alterations in molecular structure. However, the molecular weight (Mw) was reduced with increasing age, from ~4.1 × 106 to ~2.1 × 106 Da from stage 1 to stage 3, respectively. This decrease in Mw (and size) consequently reduced the shear viscosity (ηs-Stage 1 > Î·s-Stage 2 > Î·s-Stage 3). However, the extent of shear-thickening and uniaxial extensional viscosity of MP stage 2 was greater than MP stage 1, which was attributed to a greater intermolecular interaction occurring in the former. Shear-thickening behaviour was not observed in MP stage 3.

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Ionomers are associative polymers with diverse applications ranging from selective membranes and high-performance adhesives to abrasion- and chemical-resistant coatings, insulation layers, vacuum packaging, and foamed sheets. Within equilibrium melt, the ionic or associating groups are known to form thermally reversible, associative clusters whose presence can significantly affect the system's mechanical, viscoelastic, and transport properties. It is, thus, of great interest to understand how to control such clusters' size distribution, shape, and stability through the designed choice of polymer architecture and the ionic groups' fraction, arrangement, and interaction strength. In this work, we represent linear associating polymers using a Kremer-Grest type bead-spring model and perform large-scale MD simulations to explore the effect of polymer chain-length (l) and fraction (fs) of randomly placed associating groups on the size distribution and stability of formed clusters. We consider different chain-lengths (below and above entanglement), varying fractions of associating groups (represented by 'sticky' beads) between 5 and 20%, and a fixed sticky-sticky nonbond interaction strength of four times that between regular non-associating beads. For all melts containing associating groups the equilibrium structure factor S(q) displays a signature ionomer peak at low wave vector q whose intensity increases with increasing fs and l. The average cluster size Nc increases with fs. However, the effect of chain-length on Nc appears to be pronounced only at higher values of fs. Under extensional flows, the computed stress (and viscosity) is higher at higher fs and l regardless of strain rate. Beyond a critical strain rate, we observe fragmentation of the associative clusters, which has interesting effects on the stress/viscous response.

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Correlation was investigated between instrumental characteristics obtained by extension rheological or tribological measurements and human perception while swallowing using aqueous solutions of xanthan gum and locust bean gum. Extension viscosity and the friction coefficient were measured using a capillary breakup rheometer and a rotation tribometer, respectively, as in our previous study. Results were compared with shear viscosity to clarify novelty and advantage of these mechanical parameters. It was indicated that perceived cohesiveness correlated the highest with the maximum extension viscosity immediately after the onset of extensional flow, perceived spinnability correlated with extension viscosity in high Hencky strain region, and perceived sliminess correlated with the friction coefficient at the critical point between the boundary lubrication and the mixed lubrication. These correlations were discussed and tried to validate considering biomechanics of human swallowing and food-human interactions.

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Instrumental characteristics from extensional rheology and tribology for aqueous xanthan gum (XG) and locust bean gum (LBG) solutions were studied in the presence or absence of simulated saliva. Extensional viscosity was calculated from the filament shrinkage behavior using a capillary breakup extensional rheometer, whereas the friction coefficient was measured using a set-up consisting of polydimethylsiloxane substrate and a glass ball bearing on a rotational rheometer. Increase in extensional viscosity was detected immediately after initiation of extensional flow, particularly XG, and also immediately before the filament rupture, particularly LBG. Extensional viscosity tended to decrease with increased addition of simulated saliva for XG, while to increase for LBG. In both cases, effect of cations in the saliva was greater than that of mucin. From the shape of the Stribeck curve (i.e., dependence of the friction coefficient on the entrainment speed) and comparison of the friction coefficient itself, lubricity of XG was greater than that of LBG. Simulated saliva added decreased the friction coefficient for each polysaccharide through functions of cations rather than mucin. Extensional viscosity and tribological measurements revealed mechanical properties of polysaccharide solutions which cannot be determined or quantified by shear viscosity alone.

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Currently, plastic packaging represents a global challenge and has become a key point of attention for governments, media and consumers due to the visibility of the waste it generates. Despite their high resource efficiency, the perceived non-recyclability of polymeric films risks precluding them from being a relevant packaging solution in a circular economy approach. In this regard, the aim of this study was to implement a strategy to try closing the loop, via the mechanical recycling of post-consumer flexible packaging of small size (denoted as Fil-s) to obtain new films. In particular, two lots of Fil-s were used, which are PE/PP blends differing for the PP content and the presence of polar contaminants. The suitability for film blowing extrusion of these recycled materials, as such and after the addition of a compatibilizer and/or a lamellar nanosilicate, was evaluated. It was first evidenced that the difficulty of producing blown films with the pristine recycled materials, due to the frequent bubble breakages, occurring even at low draw ratios. Moreover, the shear and extensional rheological behavior of all Fil-s based systems was usefully correlated with their processability features, evidencing the key roles of the nanofiller to stabilize the bubble and of the compatibilizer to ensure a uniform film deformation, avoiding its premature breakage. Even if the adopted upgrading strategies allowed the production of blown films with both types of Fil-s, the different components of the recycled matrices were proven to significantly affect their processability and final film performances.

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OBJECTIVE: Cosmetic emulsions containing hyaluronic acid are ubiquitous in the cosmetic industry. However, the addition of (different molecular weight) hyaluronic acid can affect the filament stretching properties of concentrated emulsions. This property is often related to the "stringiness" of an emulsion, which can affect the consumer's choice for a product. It is thus very important to investigate and predict the effect of hyaluronic acid on the filament stretching properties of cosmetic emulsions. METHODS: Model emulsions and emulsions with low and high molecular weights are prepared and their filament stretching properties are studied by the use of an extensional rheometer. Two different stretching speeds are employed during the stretching of the emulsions, a low speed at 10 µm/s and a high speed at 10 mm/s. The shear rheology of the samples is measured by rotational rheology. RESULTS: We find that filament formation only occurs at high stretching speeds when the emulsion contains high molecular weight hyaluronic acid. The formation of this filament, which happens at intermediate states of the break-up, coincides with an exponential decay in the break-up dynamics. The beginning and end of the break-up of high molecular weight hyaluronic acid emulsions show a power law behaviour, where the exponent depends on the initial stretching rate. At a lower stretching speed, no filament is observed for both high molecular weight and low molecular weight hyaluronic acid emulsions and the model emulsion. The emulsions show a power law behaviour over the whole break-up range, where the exponent also depends on the stretching rate. No significant difference is observed between the shear flow properties of the emulsions containing different molecular weights hyaluronic acid. CONCLUSION: In this work, we underline the importance of the molecular weight of hyaluronic acid on the elongational properties of concentrated emulsions. The filament formation properties, for example the stringiness, of an emulsion is a key determinant of a product liking and repeat purchase. Here, we find that high molecular weight hyaluronic acid and a high stretching speed are the control parameters affecting the filament formation of an emulsion.

OBJECTIF: Les émulsions contenant de l'acide hyaluronique sont omniprésentes dans l'industrie cosmétique. En particulier, l'ajout d'acide hyaluronique (de poids moléculaires différents) peut affecter les propriétés extensionnelles d'un filament d'émulsion concentrée. Cette propriété importante est souvent assimilée à la perception organo-sensorielle "filante/cohésive" d'une émulsion et peut influer sur le choix final du consommateur pour un produit. Il est donc important d'étudier, mais aussi de pouvoir prédire, l'effet de l'acide hyaluronique sur les propriétés d'étirement de filaments d'émulsions cosmétiques. MÉTHODES: Nous avons préparé des émulsions modèles à faible et grands poids moléculaires et étudié leurs propriétés extensionnelles à l'aide d'un rhéomètre extensionnel. Deux vitesses d'étirement différentes sont utilisées, une vitesse faible à 10 µm/s et une vitesse élevée à 10 mm/s. La rhéologie de cisaillement des échantillons est mesurée par rhéologie rotationnelle. RÉSULTATS: Nous constatons que la formation de filaments ne se produit que pour des vitesses d'étirement élevées et lorsque l'émulsion contient de l'acide hyaluronique à grands poids moléculaire. La formation de ce filament, qui se produit à des temps intermédiaires de la rupture, coïncide avec une décroissance exponentielle de la dynamique de rupture. Le début et la fin de la rupture des émulsions d'acide hyaluronique de grands poids moléculaire montrent un comportement en loi de puissance, où l'exposant dépend de la vitesse d'étirement initiale. À une vitesse d'étirement inférieure, aucun filament n'est observé, à la fois pour les émulsions d'acide hyaluronique à grands et faibles poids moléculaires, mais aussi pour l'émulsion modèle ne contenant pas d'acide hyaluronique. Les émulsions présentent un comportement en loi de puissance sur tout le régime de rupture, où l'exposant dépend également de la vitesse d'étirement. Aucune différence significative n'est observée quant aux propriétés d'écoulement de cisaillement des émulsions contenant différents poids moléculaires d'acide hyaluronique. CONCLUSION: Dans cette étude, nous soulignons l'importance du poids moléculaire de l'acide hyaluronique sur les propriétés extensionnelles d'émulsions concentrées. Les propriétés de formation de filaments, ou la perception filante/cohésive d'une émulsion, sont un facteur clé dans l'appréciation d'un produit afin d'assurer un achat répété. Nous démontrons que la présence d'acide hyaluronique à grands poids moléculaires ainsi qu'une vitesse d'étirement élevée, sont les paramètres de contrôle affectant la formation de filaments dans une émulsion.

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The molecular architecture and rheological behavior of linear and branched polybutylene succinate blends have been investigated using size-exclusion chromatography, small-amplitude oscillatory shear and extensional rheometry, in view of their processing using cast and blown extrusion. Dynamic viscoelastic properties indicate that a higher branched polybutylene succinate amount in the blend increases the relaxation time due to an increased long-chain branching degree. Branched polybutylene succinate exhibits pronounced strain hardening under uniaxial elongation, which is known to improve processability. Under extensional flow, the 50/50 wt % blend exhibits the same behavior as linear polybutylene succinate.

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The rheological behaviour of dough during the breadmaking process is strongly affected by the accumulation of yeast metabolites in the dough matrix. The impact of metabolites in yeasted dough-like concentrations on the rheology of dough has not been characterised yet for process-relevant deformation types and strain rates, nor has the effect of metabolites on strain hardening behaviour of dough been analysed. We used fundamental shear and elongational rheometry to study the impact of fermentation on the dough microstructure and functionality. Evaluating the influence of the main metabolites, the strongest impact was found for the presence of expanding gas cells due to the accumulation of the yeast metabolite CO2, which was shown to have a destabilising impact on the surrounding dough matrix. Throughout the fermentation process, the polymeric and entangled gluten microstructure was found to be degraded (-37.6% average vessel length, +37.5% end point rate). These microstructural changes were successfully linked to the changing rheological behaviour towards a highly mobile polymer system. An accelerated strain hardening behaviour (+32.5% SHI for yeasted dough) was promoted by the pre-extension of the gluten strands within the lamella around the gas cells. Further, a strain rate dependency was shown, as a lower strain hardening index was observed for slow extension processes. Fast extension seemed to influence the disruption of sterically interacting fragments, leading to entanglements and hindered extensibility.

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Exopolysaccharides (EPS) synthesized by lactic acid bacteria during fermentation significantly affect the rheology of set-style acid milk gels and that of acid gel suspensions, produced from the gels by stirring. In this study, shear and uniaxial extensional flow of acid gel suspensions made with seven single strains of Streptococcus thermophilus or Lactococcus lactis was investigated. Six strains produced ropy EPS, and maximum filament length determined by using a continuous stretching method was up to four times higher than filament length of an EPS-negative control strain. The systems containing ropy EPS showed a different response to shear and extensional deformation. In shear rheology, higher apparent viscosities and an enhanced structural breakdown was observed for acid gel suspensions with more pronounced ropiness. Breakup time and extensional viscosity, determined by using a Capillary Breakup Extensional Rheometer (CaBER™), significantly increased with increasing ropiness. The increase of extensional viscosity with increasing ropiness was, however, much higher than the effects of ropiness on shear viscosity. As relaxation times also depended on ropiness, it is concluded that ropiness is caused by EPS-EPS interactions that can be better discriminated in extensional rheology. PRACTICAL APPLICATIONS: To improve the texture of fermented milk, lactic acid bacteria that are able to produce ropy exopolysaccharides (EPS) are increasingly used in the dairy industry. The EPS exhibit a significant influence on processing properties and sensory characteristics of the resulting products, which can be estimated by means of shear and extensional rheology. The current work provides information on these respective properties of acid gel suspensions, which facilitate product design by supporting the selection of appropriate starter cultures.

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Delayed capillary break-up of viscoelastic filaments presents scientific and technical challenges relevant for drop formation, dispensing, and adhesion in industrial and biological applications. The flow kinematics are primarily dictated by the viscoelastic stresses contributed by the polymers that are stretched and oriented in a strong extensional flow field resulting from the streamwise gradients created by the capillarity-driven squeeze flow. After an initial inertiocapillary (IC) or viscocapillary (VC) regime, where elastic effects seem to play no role, the interplay of capillarity and viscoelasticity can lead to an elastocapillary (EC) response characterized by exponentially-slow thinning of neck radius (extensional relaxation time is determined from the delay constant). Less frequently, a terminal visco-elastocapillary (TVEC) response with linear decay in radius can be observed and used for measuring terminal, steady extensional viscosity. However, both IC/VC-EC and EC-TVEC transitions are inaccessible in devices that create stretched necks by applying a step strain to a liquid bridge (e.g., capillary breakup extensional rheometer). In this study, we use dripping-onto-substrate rheometry to obtain radius evolution data for unentangled polymer solutions. We deduce that the plots of transient extensional viscosity vs. Hencky strain (scaled by the respective values at the EC-TVEC transition) emulate the functional form of the birefringence-macromolecular strain relationship based on Peterlin's theory. We quantify the duration and strain between the IC/VC-EC and the EC-TVEC transitions using measures we term elastocapillary span and elastocapillary strain increment and find both measures show values directly correlated with the corresponding variation in extensional relaxation time.

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Comb and bottlebrush polymers present a wide range of rheological and mechanical properties that can be controlled through their molecular characteristics, such as the backbone and side chain lengths as well as the number of branches per molecule or the grafting density. This review investigates the impact of these characteristics specifically on the zero shear viscosity, strain hardening behavior, and plateau shear modulus. It is shown that for a comb polymer with an entangled backbone and entangled side chains, a maximum in the strain hardening factor and minimum in the zero shear viscosity η0 can be achieved through selection of an optimum number of branches q. Bottlebrush polymers with flexible filaments and extremely low plateau shear moduli relative to linear polymers open the door for a new class of solvent-free supersoft elastomers, where their network modulus can be controlled through both the degree of polymerization between crosslinks, nx , and the length of the side chains, nsc , with G B B 0 ≈ ρ k T n x - 1 ( n s c + 1 ) - 1 .

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This is an investigation of the shear and extensional properties of okra polysaccharide-saliva mixtures, intended to model the mechanical behavior a food hydrocolloid during oral processing. Shear measurements show that incorporation of okra mucilage in saliva interferes with the self-assembly of salivary mucins, with partly detrimental effects on the low-shear viscosity of the mixture. This is counter-acted by excluded volume effects, as the overall concentration of macromolecules in the mixture reaches the semi-dilute regime. Particle tracking confirms the lack of direct interactions between the two polymeric populations. The contribution of extensional viscosity to the overall behavior of okra hydrocolloid-saliva mixtures is dominant, at about one to two orders of size higher than the equivalent shear values. The Trouton ratio values are in the order of tens or hundreds for the range of concentrations and deformation rates under study. Although the extensional viscosity dominates viscous flow, the two types of flow are equally important concerning the elastic behavior, giving insight on the mechanical behavior of mucilages in the oral cavity.

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The linear and nonlinear oscillatory shear, extensional and combined rheology-dielectric spectroscopy of hybrid polymer nanocomposites for semiconductive applications were investigated in this study. The main focus was the influence of processing conditions on percolated poly(ethylene-butyl acrylate) (EBA) nanocomposite hybrids containing graphite nanoplatelets (GnP) and carbon black (CB). The rheological response of the samples was interpreted in terms of dispersion properties, filler distortion from processing, filler percolation, as well as the filler orientation and distribution dynamics inside the matrix. Evidence of the influence of dispersion properties was found in linear viscoelastic dynamic frequency sweeps, while the percolation of the nanocomposites was detected in nonlinearities developed in dynamic strain sweeps. Using extensional rheology, hybrid samples with better dispersion properties lead to a more pronounced strain hardening behavior, while samples with a higher volume percentage of fillers caused a drastic reduction in strain hardening. The rheo-dielectric time-dependent response showed that in the case of nanocomposites containing only GnP, the orientation dynamics leads to non-conductive samples. However, in the case of hybrids, the orientation of the GnP could be offset by the dispersing of the CB to bridge the nanoplatelets. The results were interpreted in the framework of a dual PE-BA model, where the fillers would be concentrated mainly in the BA regions. Furthermore, better dispersed hybrids obtained using mixing screws at the expense of filler distortion via extrusion processing history were emphasized through the rheo-dielectric tests.

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The rheological properties of synovial fluid (SF) are largely attributed to the presence of high molecular weight hyaluronan (HA). However, rheological differences between SF and pure HA solutions suggest that SF proteins actively contribute towards the bulk viscoelasticity of this biological fluid. Due to various experimental challenges involved with the rheometry of low-viscosity biological fluids, the macromolecular interactions in SF and their relative rheological importance are still a matter of active discussion. Interestingly however, recent evidence suggests that the concentration and structure of proteoglycan 4 (PRG4, also known as lubricin) can directly modulate the viscoelastic properties of HA-PRG4 solutions. The objective of this review is to highlight recent rheological studies that examine the macromolecular interactions between HA and proteins in SF. First, a general overview of the chemical composition of SF and the molecular structure of its key constituents HA and PRG4 is provided. Subsequently, diverse rheological experimental techniques that have been developed to characterize HA solutions are discussed. Finally, rheological investigations of macromolecular interactions between HA, serum proteins, and PRG4 are examined. This review illustrates how diverse rheological techniques can expand our understanding of the composition-structure-function relationships in SF.

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Mamaku gum is a polysaccharide extracted from the fronds of the black tree fern found in New Zealand. The cooked pith has traditionally been used for various medicinal purposes and as a food source by the Maori people of New Zealand. It has potential applications as a thickener in the food industry and as a palliative for patients with dysphagia. Studies on the shear rheology of Mamaku gum have revealed that the gum exhibits shear thickening at a critical shear rate due to a transition from intra- to inter-molecular chain interactions upon shear-induced chain elongation. In this paper, we demonstrate that these interactions are primarily due to hydrogen bonding. We perform extensional rheology on mixtures of Mamaku gum and urea (a known disruptor of hydrogen bonds) to quantify the nature of these interactions. Capillary Breakup Extensional Rheometry (CaBER) performed on the pure Mamaku gum solutions yield plateau values of the Trouton ratio as high as ∼10(4), showing that the viscoelasticity of the gum in uniaxial elongation is much higher than in shear. For all Mamaku concentrations tested, the extensional viscosity decreases upon increasing urea concentration. Furthermore, the relaxation time decreases exponentially with increasing urea concentration. This exponential relationship is independent of the Mamaku concentration, and is identical to the relationships between urea concentration and characteristic timescales measured in nonlinear shear rheology. We show using the sticky reptation model for polymers with multiple sticker groups along the backbone how such a relationship is consistent with a linear decrease in the free energy for hydrogen bond dissociation. We then demonstrate that a time-concentration superposition principle can be used to collapse the viscoelastic properties of the Mamaku-gum/urea mixtures.

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